The present invention generally relates to systems for storing and reading out musical tone signals, and more particularly to a system for storing (recording) a musical tone signal which is produced by a musical instrument into a memory and reading out (reproducing) the stored musical tone signal to generate a musical tone.
As one tyoe of electronic musical instrument, an apparatus was devised in which a musical tone signal produced by a musical instrument such as piano, guitar, and percussion instrument, is stored in a memory, and the stored musical tone signal is reproduced upon playing of the electronic musical instrument. According to such an electronic musical instrument, a musical tone exceedingly similar to the musical tone produced by the actual musical instrument is reproduced upon playing of the electronic music instrument. Each of the sounds in the musical scale of the actual musical instrument are respectively stored in corresponding memories by the manufacturer of the electronic musical instrument. When the player of the electronic musical instrument presses a key of a keyboard, for example, a musical tone signal is read out from a corresponding memory and reproduced as a musical tone. According to this type of an electronic musical instrument, the reproduced sounds are exceedingly similar to those of the actual musical instrument, when compared to conventional electronic musical instruments which produce synthesized sounds.
When storing the musical tone signal of the actual musical instrument, the musical tone signal is sampled and converted into a digital signal. In order to truely reproduce the musical tone signal, it is necessary to sample the musical tone signal at a frequency which is twice the maximum frequency included within the musical tone signal. However, the sound (musical tone) produced by the musical instrument does not only include the fundamental wave, but also includes high orders of harmonics of the fundamental wave. Thus, the maximum frequency of the frequency components included within one musical tone is exceedingly high compared to its fundamental frequency. Moreover, the musical tone is not an instantaneous sound, and is a sound which assumes a high level at the instant when the musical tone is produced and gradually becomes attenuated with time.
Accordingly, if the sampling is to be performed not only with respect to the fundamental wave frequency, but also including the high order harmonic frequencies, the sampling must be performed at twice the maximum frequency. Further, such sampling must be continued even while the sound level becomes attenuated under a certain level. As a result, the memory for storing the musical tone signal sampled in the above described manner required a considerably large memory capacity, and there was a disadvantage in that the manufacturing cost of the electronic musical instrument became high.
As will be described hereinafter, the musical tone becomes attenuated from the instant when the musical tone is produced, however, the attenuation rate is not the same for the low frequency range (fundamental wave) component and the high frequency range (harmonic) components. That is, the low frequency range component gradually becomes attenuated within a long period of time, but on the other hand, the high frequency range components become attenuated within a short period of time. The attenuation time becomes shorter as the frequency becomes higher. Hence, when storing the sampled musical tone signal into the memory, the present inventor noted that it was meaningless to continue the sampling at a high sampling frequency which was set by taking into account the maximum frequency component obtained immediately after the musical tone is produced, after a certain time period has elapsed from the instant when the musical tone was produced and the high frequency range components have been rapidly attenuated.